Power generation apparatus using permanent-magnet generator

ABSTRACT

A power generation apparatus includes a permanent-magnet AC generator, a first converter for converting AC power into DC power, and a second converter for converting the DC power produced by the first converter into AC power. The first converter includes a unit for controlling active power and a unit for controlling reactive power and the second converter includes a unit for controlling a voltage of a DC system and reactive power or AC voltage of a power system.

BACKGROUND OF THE INVENTION

The present invention relates to a power generation apparatus using apermanent-magnet generator and more particularly to control of a powerconverter.

The power generation apparatus using the permanent-magnet generator usesa gas turbine, a hydropower, wave power or the like as a power source torotate the permanent-magnetic generator. AC power generated by thepermanent-magnet generator is converted into DC power by a firstconverter and the DC power produced by the first converter is convertedinto AC power by a second converter again to supply the AC power.

As a control method of the power generation apparatus using thepermanent-magnet generator, JP-A-2000-345952 discloses “a wind powermultipole generator and a wind power generation method” in which anactive power command value is decided on the basis of the rotation speedof a multipole generator to control output power of a variable speedinverter. Further, JP-A-5-22938 discloses “a control circuit of a powerconversion system” in which a power converter is controlled to make aterminal voltage of a permanent-magnet generator fixed.

In order to utilize energy obtained from the power source effectively,it is desirable to make the power generation apparatus using thepermanent-magnet generator have robust characteristics with highefficiency.

In the prior art, since the active power command value is decided on thebasis of the rotation speed of the power generator to control activepower, measures for adjusting a power factor of the power generator arenot provided and operation taking the efficiency into consideration as apower generation system is not always performed. Further, when theconstant terminal voltage is maintained, a large reactive current issupplied in order to increase the terminal voltage in the area where therotation speed of the power generator is low, so that a potentialdifference between the terminal voltage and an internal induced voltageof the power generator is increased to make a phase difference betweenthe terminal voltage and the current large and consequently reduce thepower generation efficiency.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a power generationapparatus using a permanent-magnet generator or a power generationsystem using the same having robust characteristics with high efficiencywithin a wide variable speed range in a capacity of a converter by meansof control of reactive power or a voltage of a first converter.

The power generation apparatus using the permanent-magnet generatoraccording to the present invention, includes a permanent-magnetgenerator for generating AC power, a first converter for converting theAC power generated by the generator into DC power, and a secondconverter for converting the DC power produced by the first converterinto AC power. The first converter includes means for controlling activepower of the AC power of the generator and means for controllingreactive power of the AC power of the generator, and the secondconverter includes means for producing the active power.

In the power generation apparatus using the permanent-magnet generatoraccording to the present invention, the first converter includes meansfor calculating a reactive power command value on the basis of an activepower command value and a rotation speed of the generator and the firstconverter controls reactive power of the AC power of the generator onthe basis of the active power command value and the rotation speed ofthe generator.

In the power generation apparatus using the permanent-magnet generatoraccording to the present invention, the first converter includes meansfor controlling active power of the AC power of the generator, means forcontrolling a voltage of the AC power of the generator, and means forcalculating a voltage command value on the basis of an active powercommand value and a rotation speed of the generator and the firstconverter controls a terminal voltage of the generator on the basis ofthe active power command value and the rotation speed of the generator.

A setting method of the power generation apparatus using thepermanent-magnet generator according to the present invention, includingmeans for calculating a reactive power command value on the basis of anactive power command value and a rotation speed of the generator andmeans for calculating a voltage command value on the basis of the activepower command value and the rotation speed of the generator, comprisessetting up the reactive power command value or the voltage command valueso that a phase difference between an output current of the generatorand an internal induced voltage of the generator is equal to zero inaccordance with the active power command value until a rotation speed atwhich a terminal voltage of the generator reaches a rated value isreached and setting up the reactive power command value or the voltagecommand value so that the terminal voltage is fixed in accordance withthe active power command value in the area where the rotation speed isincreased.

In the setting method of the power generation apparatus using thepermanent-magnet generator according to the present invention, the firstconverter includes means for controlling active power of the AC power ofthe generator, means for controlling a voltage of the AC power of thegenerator, and means for calculating a voltage command value on thebasis of an active power command value or the rotation speed of thegenerator, and the first converter controls a terminal voltage of thegenerator on the basis of the active power command value or the rotationspeed of the generator.

The setting method of the power generation apparatus using thepermanent-magnet generator according to the present invention, includingmeans for calculating the voltage command value on the basis of theactive power command value or the rotation speed of the generator,comprises setting up the voltage command value so that the terminalvoltage is fixed in accordance with the active power command value orthe rotation speed of the generator.

With the above configuration, there can be provided the power generationapparatus using the permanent-magnet generator having the robustcharacteristics with high efficiency while utilizing the convertercapacity effectively.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram schematically illustrating a power generationapparatus according to an embodiment 1 of the present invention;

FIG. 2 is a block diagram illustrating a control apparatus of a firstconverter used in the power generation apparatus of the embodiment 1;

FIG. 3 is a diagram explaining a relation of an reactive power commandvalue gain Kq and a PMG rotation speed N;

FIG. 4 is a diagram explaining a relation of a active power commandvalue Pr and a PMG rotation speed N;

FIG. 5 is a diagram explaining a relation of a active power commandvalue Qr and a PMG rotation speed N;

FIG. 6 is a diagram explaining a relation of a voltage command valuegain Kv and a PMG rotation speed N;

FIG. 7 is a diagram explaining a relation of a voltage command value Vrand a PMG rotation speed N;

FIG. 8 is a vector diagram for explaining a control method in a steadyrotation area;

FIG. 9 is a vector diagram explaining a control method in a high-speedrotation area; and

FIG. 10 is a diagram explaining a relation of a PMG terminal voltage Vtand a PMG rotation speed N.

DESCRIPTION OF THE EMBODIMENTS Embodiment 1

Referring now to FIG. 1, a power generation apparatus according to anembodiment is described. The power generation apparatus using apermanent-magnet generator (hereinafter abbreviated as PMG) of theembodiment uses a power source 1 such as a gas turbine, hydropower, wavepower or the like to rotate a permanent-magnet generator 2 and AC powergenerated by the permanent-magnet generator 2 is converted into DC powerby a first converter 3. The DC power produced by the first converter 3is again converted into AC power by a second converter 4 and the ACpower is supplied to a power system 5. Each of the first and secondconverters 3 and 4 includes, as a three phase bridge circuit, 6self-commutating semiconductor elements and 6 diodes constituting aself-commutated converter, for example. Each of the self-commutatingsemiconductor elements is connected to control apparatuses 100 and 200for inputting control pulses.

The control apparatus 100 includes a converter control unit 103 whichprepares control pulses on the basis of outputs of an active powercontrol circuit 101 and a reactive power control circuit 102 andcontrols active power and reactive power generated by thepermanent-magnet generator 2. On the other hand, the control apparatus200 includes a converter control unit 203 which prepares control pulseson the basis of outputs of a DC voltage control circuit 201 and areactive power control circuit or an AC voltage control circuit 202 andcontrols voltage of a DC system and reactive power or an AC voltage ofthe power system 5.

The control apparatus 100 of the first converter of the embodiment isnow described in detail with reference to FIG. 2. The control apparatus100 takes in a rotation speed N of the PMG detected by a rotation speeddetection circuit 21, three-phase terminal voltages Vta, Vtb and Vtc ofthe PMG detected by a voltage detection circuit 22 and three-phaseoutput currents Ia, Ib and IC of the PMG detected by a current detectioncircuit 23 and calculates active power Pf and reactive power Qf from thefollowing equations (1), (2) and (3). The positive direction of theactive power is defined by the power generation direction of the PMG andthe positive and negative directions of the reactive power are definedby the leading direction and the lagging direction thereof,respectively. $\begin{matrix}{\begin{bmatrix}{{vt}\quad \alpha} \\{{vt}\quad \beta}\end{bmatrix} = {2/{{3\begin{bmatrix}1 & {{- 1}/2} & {{- 1}/2} \\0 & {{{SQRT}(3)}/2} & {{- {{SQRT}(3)}}/2}\end{bmatrix}}\begin{bmatrix}{vta} \\{vtb} \\{vtc}\end{bmatrix}}}} & (1) \\{\begin{bmatrix}{1\quad \alpha} \\{1\beta}\end{bmatrix} = {2/{{3\begin{bmatrix}1 & {{- 1}/2} & {{- 1}/2} \\0 & {{{SQRT}(3)}/2} & {{- {{SQRT}(3)}}/2}\end{bmatrix}}\begin{bmatrix}{1a} \\{1b} \\{1c}\end{bmatrix}}}} & (2) \\{{\begin{bmatrix}{Pf} \\{Qf}\end{bmatrix} = {\begin{bmatrix}{1\quad \alpha} & {1\quad \beta} \\{1\quad \beta} & {{- 1}\quad \alpha}\end{bmatrix}\quad\begin{bmatrix}{{vt}\quad \alpha} \\{{vt}\quad \beta}\end{bmatrix}}}\quad} & (3)\end{matrix}$

The active power control circuit 101 controls so that the active powerPf is equal to an active power command value Pr. A reactive powercommand value setting circuit 104 sets up a reactive power command valueQr on the basis of the active power command value Pr and the rotationspeed N of the PMG and the reactive power control circuit 102 controlsso that the reactive power Qf is equal to the command value Qr. Theactive power control circuit 101 and the reactive power control circuit102 use PI (proportion and integration) control or the like. Theconverter control unit 103 prepares control pulses on the basis ofoutputs of the active power control circuit 101 and the reactive powercontrol circuit 102 and supplies on-and-off signals for switching theself-commutating semiconductor elements to the first converter 3.

A setting method of the reactive power command value setting circuit 104of the present invention is now described. FIG. 3 shows a relation of areactive power command value gain Kq and the rotation speed N of thePMG. The rotation speed of the PMG at which that a terminal voltagereaches a rated value is defined to N1. The reactive power command valuegain Kq is set up to a positive value until the rotation speed N1 isreached and the reactive power command value gain Kq is varied from thepositive value to a negative value from after the rotation speed N1until a rotation speed N2 at which a lagged reactive power is increasedto a maximum output is reached. The gain Kq is set up to a fixednegative value after the rotation speed N2. ±Kq1 is set up to any valuein accordance with characteristics of the power source 1, thepermanent-magnet generator 2 or the like so that the maximum commandvalue Qr does not exceed the maximum output point of the reactive powerand the reactive power command value gain Kq is decided in accordancewith the rotation speed N of the PMG.

FIG. 4 shows an example of a relation of the active power command valuePr and the rotation speed N of the PMG. The active power command valuePr can adopt a value in the hatched area in accordance with the rotationspeed when the rated value thereof is Pr1. The reactive power commandvalue Qr is expressed by the following equation (4) from the reactivepower command value gain Kq and the active power command value Pr.

 Qr=Qo+Kq·Pr  (4)

FIG. 5 shows an example of a relation of the reactive power commandvalue Qr and the rotation speed N of the PMG. The reactive power commandvalue Qr can adopt a value in the hatched area of FIG. 5 on the basis ofthe reactive power command value gain Kq determined by the active powercommand value Pr and the rotation speed N of the PMG and is a commandvalue to the reactive power control circuit 102. When it is assumed that±Kq1=±1.0 and Pr1=1.0 PU, ±Qr1 is +(leading)1.0 PU and −(lagging)1.0 PU.A reactive power command initial value Qo is set up to zero in theembodiment, while it can be set up to any value in accordance withconditions of the power source 1, the permanent-magnet generator 2 andthe like similarly to the reactive power command value gain Kq. Thereactive power command value setting circuit 104 decides the reactivepower command value Qr by using the characteristic of FIG. 3 and thefollowing equation (5).

FIG. 6 shows an example of a relation of a voltage command value gain Kvand the rotation speed N of the PMG. The voltage command value gain Kvis increased to Kv1 until the rotation speed N1 is reached. The voltagecommand value gain Kv is set up to a fixed Kv1 after the rotation speedN1 has been reached and is decided in accordance with the rotation speedN. Further, a voltage command value Vr is expressed by the followingequation from the voltage command value gain Kv and the active powercommand value Pr.

Vr=Vo+Kr·Pr  (5)

Next, a control method of the embodiment is described with reference tovector diagrams of FIGS. 8 and 9 and FIG. 10. FIG. 8 is a vector diagramshowing a control method in a low-speed rotation area.

That is, the low-speed rotation area is an area from zero to N1 of therotation speed of the PMG. In FIG. 8, Eo represents an induced voltage,X a generator leakage reactance, I an output current and Vt a terminalvoltage of the generator. Since the internal induced voltage Eo of thegenerator is increased in proportion to the rotation speed, the firstconverter 3 uses the control apparatus 100 to decide the reactive powercommand value Qr or the voltage command value Vr so that phases of theoutput current I of the generator and the internal induced voltage Eo ofthe generator are coincident with each other and control the terminalvoltage Vt of the generator. Consequently, the power factor of thegenerator is improved and high efficiency of the power generationapparatus in the low-speed rotation area can be attained.

FIG. 9 is a vector diagram showing a control method in a high-speedrotation area.

That is, the high-speed rotation area is an area where the rotationspeed of the PMG is larger than N1. Since the terminal voltage Vt of thegenerator has already reached the rated value at the rotation speed N1as described above, the power generation apparatus is stopped due toover-voltage if the rotation speed is increased as it is. Accordingly,the first converter 3 uses the control apparatus 100 to decide thereactive power command value Qr or the voltage command value Vr so thatthe output current I of the generator is lagged behind the internalinduced voltage Eo of the generator and control the terminal voltage Vtof the generator. Consequently, a variable speed range of the generatorin the high-speed rotation area can be widened.

FIG. 10 shows a relation of the terminal voltage Vt and the rotationspeed N of the PGM. C1 represents the relation in case where thereactive power or voltage is not controlled and C2 represents therelation according to the present invention. In the low-speed rotationarea, that is, in the area where the rotation speed is zero to N1, theterminal voltage is controlled to be higher than C1 in order to satisfythe relation of the vector diagram shown in FIG. 8. Further, in thehigh-speed rotation area, that is, in the area where the rotation speedis N1 to N2, the terminal voltage is maintained to the rated value Vt1so that the variable speed range of the generator is widened and afterthe rotation speed exceeds N2, the voltage is increased again since thereactive power which the converter can produce is increased to themaximum.

Embodiment 2

The embodiment is the same as the embodiment 1 with the exception thatthe reactive power control circuit 102 and the reactive power commandvalue setting circuit 104 of FIG. 2 are replaced by a voltage controlcircuit and a voltage command value setting circuit, respectively, andthe voltage command value setting circuit decides the voltage commandvalue Vr on the basis of the active power command value Pr and therotation speed N of the PGM, the voltage control circuit 102 controllingso that the terminal voltage Vt of the PMG is equal to the command valueVr, the terminal voltage Vt of the PMG being calculated by the followingequation (6):

Vt=SQRT(Vtα ² +Vtβ ²)  (6)

The voltage control circuit uses the PI (proportion and integration)control in the same manner as described above.

FIG. 7 shows an example of a relation of the voltage command value Vrand the rotation speed N ocf the PMG. The voltage command value Vr isset up to a value in the hatched area of FIG. 7 on the basis of theactive power command value Pr and the voltage command value gain Kvdetermined from the rotation speed N of the PMG and becomes a commandvalue to the voltage control circuit. Vr1 is 1.0 PU when Kv=1.0 andPr1=1.0 PU, for example. The setting method of the voltage commandinitial value Vo and the realization method by the equation (6) and thecharacteristic of FIG. 6 are the same as those of the reactive powercommand value setting circuit 104 of the embodiment 1.

Further, in the case of the power generation apparatus in which energyof the power source is transmitted to the PMG stably as a gas turbine,for example, since the active power substantially proportional to therotation speed of PMG is obtained, any of the active power command valuePr or the rotation speed N of the PMG may be inputted to the voltagecommand value setting circuit. That is, in this case, when the voltagecommand value Vr is determined on the basis of any of the active powercommand value Pr or the rotation speed N of the PMG, there are obtainedthe same effects as the case where both of the active power commandvalue Pr and the rotation speed N of the PMG are used.

According to the present invention, the efficiency of thepermanent-magnet generator can be enhanced and the variable speed rangecan be widened by control of the reactive power or voltage of the powerconverter and there can be provided the power generation apparatushaving the robust characteristics with high efficiency while utilizingthe converter capacity effectively.

It should be further understood by those skilled in the art that theforegoing description has been made on embodiments of the invention andthat various changes and modifications may be made in the inventionwithout departing from the spirit of the invention and the scope of theappended claims.

What is claimed is:
 1. A power generation apparatus including apermanent-magnet generator for generating AC power, a first converterfor converting the AC power generated by said generator into DC power,and a second converter for converting the DC power produced by saidfirst converter into AC power, wherein: said first converter includesself-commutating semiconductor elements, means for controlling an activepower component of the AC power of said generator and means forcontrolling a reactive power component of the AC power of saidgenerator; and said second converter includes self-commutatingsemiconductor elements and means for producing a first active power. 2.A power generation apparatus according to claim 1, wherein: said firstconverter includes means for calculating a reactive power command valueon the basis of an active power command value and a rotation speed ofsaid generator; and said first converter controls the reactive powercomponent of the AC power of said generator on the basis of the activepower command value and the rotation speed of said generator.
 3. A powergeneration apparatus including a permanent-magnet generator forgenerating AC power, a first converter for converting the AC powergenerated by said generator into DC power, and a second converter forconverting the DC power produced by said first converter into AC power,wherein: said first converter includes self-commutating semiconductorelements, means for controlling an active power component of the ACpower of said generator, means for controlling a voltage of the AC powerof said generator, and means for calculating a voltage command value onthe basis of an active power command value and a rotation speed of saidgenerator; and said first converter controls a terminal voltage of saidgenerator on the basis of the active power command value and therotation speed of said generator.
 4. A power generation apparatusincluding a permanent-magnet generator for generating AC power, a firstconverter for converting the AC power generated by said generator intoDC power, and a second converter for converting the DC power produced bysaid first converter into AC power, wherein: said first converterincludes self-commutating semiconductor elements, means for controllingan active power component of the AC power of said generator, means forcontrolling a voltage of the AC power of said generator, and means forcalculating a voltage command value on the basis of an active powercommand value or a rotation speed of said generator; and said firstconverter controls a terminal voltage of said generator on the basis ofthe active power command value or the rotation speed of said generator.5. A power generation apparatus according to claim 2, wherein: when saidfirst converter calculates said reactive power command value on thebasis of the active power command value and the rotation speed of saidgenerator; the reactive power command value and the active power commandvalue are set up so that phases of an output current of said generatorand an internal induced voltage of said generator are coincident witheach other, in accordance with the rotation speed of said generator in alow-speed rotation area of said generator; and the reactive powercommand value and the active power command value are set up so that theoutput current of said generator lags behind the internal inducedvoltage in said generator, in accordance with the rotation speed of saidgenerator in a high-speed rotation area of said generator.
 6. A powergeneration apparatus according to claim 3, wherein: when said firstconverter calculates said voltage command value on the basis of theactive power command value and the rotation speed of said generator, thevoltage command value and the active power command value are set up sothat phases of an output current of said generator and an internalinduced voltage of said generator are coincident with each other inaccordance with the rotation speed of said generator in a low-speedrotation area of said generator; and the voltage command value and theactive power command value are set up so that the output current of saidgenerator lags behind the internal induced voltage in said generator inaccordance with the rotation speed of said generator in a high-speedrotation area of said generator.